It is known that dust removal by filtration can also be used for desulphurization. In that case alkaline additives such as calcium hydroxide are added to the gas stream in order to bind sulphur oxides (W. Schulte.beta., Brennstoff-Warme-Kraft, Vol. 36 (1984), No. 10, p. 420-426). After reaction, these additives must be removed, together with the dust, from the gas stream. To this end, fabric filters are used so that filtration takes place within and on the forming filter cake. It has been found that the reaction of Ca(OH).sub.2 with SO.sub.2 is substantially boosted by continued reaction in the filter.
In fabric filters, however, an irreversible deposit of ultrafine particles in the filter fabric takes place (irreversible partial plugging). The resulting high pressure drop and high cleaning-cycle frequency result in excessive wear. Furthermore, the known fabric filters can only be run at operation temperatures of up to approx. 250.degree. C. (W. Schulte.beta., Brennstoff-Warme-Kraft, Vol. 36 (1984), No. 10, p. 422), and in particular in case of high solids concentrations, an upstream preliminary separation step may become necessary.